Electromagnetic relay structure



April 28, 1970 w. D. MAYNARD E 3,509,502

' ELECTROMAGNETIC RELAY STRUCTURE Filed Nov. '2, 19s? .4 Sheets-Sheet 1FIG. I

INVENTORS W. D. MAYNARD E. A. BELANGER THEIR ATTORNEY April Z8,197O Q w.|v ETAL 3,509,502

ELECTROMAGNETIC RELAY STRUCTURE Filed Nov. '7, 1967 I )4 Sheets-Sheet 2FIG. 2 FIG. 3

E g 1 5% E 53 Q; E" =5 =E= low 1 =5? 5* L 24 R649 7 p) INVENTORS D.MAYNARD A. BE LANGER THEIR ATTORNEY April 28, 1970 w. p. MAYNARD E- L3,509,502

ELECTROMAGNETIC RELAY STRUCTURE Filed Nov. 7, 19a"! .4 Shets-Sheet 5FIG. 4 HG 5 66 7| 10 66 m ig a 3 E35 72 @272 zit- 7'. 18 :1? 3$] 76. 13:E E E E3 E E FIG. 9 |o 113 INVENTORS w. 0. MAYNARD E. A. BELANGER BY WTHEIR ATTORNEY April 28, 1970 w. D. MAYNARD EAL ELECTROMAGNETIC RELAYSTRUCTURE .4 Sheets-Sheet 4.

Filed Nov. v, 1967 FIG. 8

ME 5 r YR INVENTORS W. D. MAYNARD E. A. BELANGER FIG. 6

THEIR ATTORNEY U.S. Cl. 335-129 11 Claims ABSTRACT OF THE DISCLOSUREThis electromagnetic relay is of the safety type as used by railroads.It has parts molded of black fiber glass plastic material and has otherparts formed of metal and constructed to be assembled in such a way asto provide a composite structure requiring no adjustment after initialassembly. The armature is mounted on a knife edge bearing with theworking airgap at the rear of the relay and the contact operator at thefront of the relay. The plastic cover holds a magnetic back yoke inplace for connecting the two magnetic core members, which back yoke isdirectly removable when the cover is removed so as to e able to replacethe coils without further disassembly. The coils have quick detachableconnectors which connect to the coil lead fingers at the front of therelay. The contact fingers are pushed into position from the front ofthe relay with the cover removed and a guide block is p rmanentlyprovided for assisting the entry of the contact fingers into the rearmounting block into which such fingers automatically lock when they areplaced in position.

BACKGROUND OF THE INVENTION The present invention relates to railroadsafety relays, and more particularly to an electromagnetic relayassembled from a multiplicity of parts and constituting an operablerelay when once assembled without further adjustment.

Heretofore, electromagnetic relays of the safety type have been builtwhich are highly efficient, but most expensive to manufacture. One ofthe reasons for the expense in manufacture is that the relay requires afine adjustment after initial assembly in order to be properlyoperative. Also, such fine adjustment of the relay tends to deteriorateand reduce the life of the relay.

The present invention relates to a safety type relay which has a gravitybiased armature for operating the contacts, which armature isadditionally biased by a suitable coil spring so as to minimize itsresponse to vibration and bounce, and also to maintain its operabilityuniform over a long life. The armature operates the contact fingers ofthe relay through a contact pusher member connected to the contactsdirectly in line with their contact points to directly oppose anytendency to stick due to fusion effects that might develop through therelay operation; and also to avoid the variable deflection of thecontact fingers.

Thus, the purpose of the present invention is to provide an improvedsafety relay which does not require adjustment after the initialassembly, and which is easily and rapidly assembled from parts that canbe mass produced and yet meet the rigid requirements necessary forsafety operations.

Another object of the present invention is to provide an improved relayassembly wherein the parts are readily assembled into precise positionsdue to the type of manufacture of the parts so as to provide the desiredoperating "United States Patent characteristics which are insensitive tominor production variations.

A further object of the invention is to provide a relay having aneflicient magnetic structure which can be quickly and readilydisassembled in part for the replacement of the coils on the relay.

SUMMARY OF INVENTION In general, the relay of this invention includes ahousing structure having the shape of a parallelepiped with rectangularbases, a lattice structure located inside the front of the housingstructure and integral therewith, the lattice structure having spacedopenings, with a guide block located in the housing structure abuttingthe lattice structure, and a slotted contact mounting block locatedwithin the housing structure at the rear of the guide block, the slotsin the contact mounting block being located to match the spaces in thelattice structure, and the guide block having internal chutes withopenings at one end matching the spaces in the lattice structure andwith openings at the other end matching the slots in the contactmounting block.

The relay of this invention is further characterized by having itshousing in the form of a rectangular box substantially open on theinside thereof with openings at the front and back and with the othersides completely enclosed, an electromagnetic structure located in thelower portion of the housing and having an L-shaped armature cooperatingtherewith, one arm of the armature cooperating with the electromagnet atthe rear of the relay to form a working airgap, and the other arm of thearmature extending forwardly through the mid portion of the housing,whereby the armature is gravity biased to normally open the workingairgap, with electrical contacts mounted in the upper portion of thehousing, and a pusher member operated by the other arm of the armaturefor operating the contacts.

The relay of the present invention is further characterized by having anL-shaped armature mounted on a knife edge bearing in exact alignmentwith the pole faces of the two cores so as to have one arm of thearmature in a working airgap with the pole faces and the other arm eX-tending through the central section of the housing structure andoperatively connected to the contacts located in the upper portion ofthe structure, windings on the two cores, and a slip-on type back yokehaving holes for snugly receiving the two cores, and a cover forenclosing the front side of the relay housing with a spring meansmounted on the inside thereof for holding the back yoke in position.

For a better understanding of the present invention together with otherand further objects thereof, reference is made to the followingdescription, taken in connection with the accompanying drawings, whileits Scope will be pointed out in the appended claims.

In the drawings:

FIG. 1 is a side elevation partially in section taken on lines 1--1 ofFIG. 2 which shows the parts of the electro magnetic relay constitutingthe structure of the present invention;

FIG. 2 is a front view with the cover of the relay removed and withparts shown in section to illustrate the assembly shown in FIG. 1;

FIG. 3 is a back view of the structure shown in FIG. 1 illustrating moreparticularly the slotted contact mounting block and the coded back coverfor the electromagnetic portion of the relay;

FIG. 4 is a front view of the housing structure only of the relay toshow the form of the structure to which all of the other parts arerelated;

FIG. is a side sectional view of the housing structure shown in FIG. 4;

FIG. 6 is an enlarged side view of the armature and its knife edgebearing;

FIG. 7 is an enlarged top view of the armature and its knife edgebearing as shown in FIG. 6;

FIG. 8 shows a front view of the contact pusher member shown in sideview in FIG. 1; and

FIG. 9 is a top view of the front cover as mounted on the housingstructure and which is held in place on a terminal board by a wire bailfitted over the handle on the cover and extending to the two recesses inthe terminal board.

Generally speaking, the electromagnetic relay of the present inventionis comprised of a molded frame or housing structure 10 Which enclosesthe various parts and to which a transparent cover 11 is attached.Inside the upper portion of the housing, the contact assembly islocated, and in the lower portion of the housing, the electromagneticstructure is located.

The armature 35 is mounted on a knife edge bearing 31 riveted onto thehousing between the upper and lower portions of the housing and near itsback. The armature 35 is L-shaped and has a portionor arm whichcooperates with the two pole faces 33 and 34 of the two cores 30 whichare rigidly attached to the housing structure. There is also a contactoperating portion or arm 35A of the armature which extends towards thefront of the housing between its upper and lower portions.

The knife edge bearing 31, the armature 35, the cores 30 and the codedback plate 36 are assembled and riveted in place in the housing at thesame time on the two vertical bosses 15 located one on each side of thelower portion of the housing. The contact operating portion of thearmature 35A rests at its forward end against the upper side of across-bridge 18 arranged in the form of an arch connecting the two sidesof the housing 10. Also, a flat cross-bridge member 16 is located at theback of the housing connecting the tops of the two vertical bosses 15.There are two horizontal ribs 19 connecting with the two vertical bossesand extending forward to the arched cross-bridge. In a similar fashion,two horizontal ribs 21 extend from the vertical bosses forward to a flatcross-bridge at the front of the housing located between the spaceallotted to the cores and coil members of the electromagnetic structure.

The first-mentioned flat cross-bridge 16 at the back of the housing andconnecting the tops of the two vertical bosses 15- has a downwardlyextending abutment 14 running crosswise directly above the armature onits knife edge bearing and acting to hold the armature downwardly onsuch knife edge bearing.

At the front of the upper portion of the housing is a honeycomb orlattice structure for providing back stops for certain fixed contactfingers and providing supports for the coil springs located to supplythe bias to such fixed contact fingers. This honeycomb or lattice alsohas a back stop for the coil spring which biases the armature to anormal position against the arched crossbridge 18. In addition, thislattice structure provides rigidity to the housing. The backupperportion of the housing is open so as to receive a contact guideblock 40 which is also of a honeycomb form. In addition, a rear contactmounting block 42 is provided with suitable slots and is bolted intoposition following the insertion of the contact guide block 40.

The contact fingers, such as finger 39, are moved into position from thefront of the housing. As they enter their respective spaces in thelattice structure at the front of the housing, they also enter therespective chutes, such as chute 44, in the contact guide block whichguides the end of the finger to enter the appropriate slot in thecontact mounting block 42 at the rear of the relay. As a small portionof this contact 39 extends out of the slot at the rear of the mountingblock 42,

a tool is used to grasp the extending end and pull it rearwardly untilthe contact finger locking member 45 springs downwardly and engages theside of the slot in the block 42. When all the contact fingers are inposi tion, the coil springs 41 are inserted into the lattice structurein a way to bias the fixed contact fingers against their respectivestops in the lattice structure. Also, the coil spring 48 for biasing thearmature is placed in position in the lattice structure.

Assuming that all of the contact fingers are in appropriate positions,the contact pusher member 51 is mounted over the armature arm 35A andeach movable contact finger is inserted in the respective slots in thepusher member 51. When the pusher member 51 is appropriately located, alock finger 53 is then slipped into position through the slot in thepusher member 51 and through the contact guide block 40 and into therear contact mounting block 42 until it is locked into position. Thislock finger 53 has projections at the front which extend to the rightand left as viewed from the front so as to hold the contact pushermember 51 in position against the rear projections on each of themovable contact fingers mounted in the pusher member.

The test fingers 64 are provided with narrow projections at each end.Each finger 64 may he slid into its appropriate position in the sliderunways provided at the base of the relay.

The two coils 28 on suitable plastic spools 38 are inserted over thecores 30 and moved into their positions. Their lead wires come out atthe front of the relay for attachment to the lead fingers 49 located atthe sides of the lattice structure. The quick detachable connectors 50actually insert through a suitable space in the pusher member 51. Whenthis has been done, a back yoke 62 is fitted onto the two extendingcores 30 with such back yoke 62 having holes for receiving the coreswhich provide a smooth and accurate fit with the core members. The cover11 is then positioned over the front of the relay to enclose theelectromagnetic portion and the contact assembly. A spring 63 is locatedin the cover to hold the back yoke tightly in position on the cores. Theplacement of the cover 11 also receives the ends of the test fingers 64through slots in the cover.

A fiat cross-bridge 69 in the cover .11 fits appropriately just abovethe winding lead connectors 50 to separate them from the movable contactfingers extending through the contact pusher member. Such cover is heldin position by suitable screws inserted into appropriate recessed holesin the corners of the cover and extending into the housing member at itsfour corners. The relay is then ready to be fitted into a suitableterminal board.

More specifically and with reference to FIG. 1, the electromagneticrelay structure is shown in a side elevational view with certain partsin section as taken in general on lines 1-1 of FIG. 2. This relaycomprises a housing structure 10 and a cover member 11. The housingstructure 10 is shown with a front view in FIG. 4 with all parts removedand in a side sectional view taken on lines 55 in FIG. 5 also with allparts removed.

Referring to FIG. 4, the housing structure 10 is molded of a fiber glassfilled resin in a single piece in the form of a rectangular box-likeshape sometimes termed a parallelepiped with rectangular bases. Suchmolding includes different compartmental separations and structure togive added strength and rigidity to the structure, as well as providingcertain functions broadly explained above.

In FIGS. 4 and 5, it can be seen that the housing struc ture 10 hasinwardly extending vertical bosses 15 along the rear inside edge on bothsides. At the top of these bosses 15 is a cross-bridge 16 which is flatand extends between the two sides of the housing 10. An upstandingcentral boss 17 is provided for receiving a screw. Around the inside ofthe wall of the housing 10 adjacent the rear edge is a depressed stripmaking the wall of the housing slightly thinner. This makes a recess forreceiving the slotted contact mounting block 42. This block 42 hasscrews inserted in the boss 17 at the bottom of the upper space orportion and also inserted in the two bosses 66 at the top (see FIG. 4).Therefore, the top fioor of the cross-bridge 16 is raised slightly oneach side of the boss 17; and similarly the underside of the sameportion is slightly raised. The abutment 14 joins these two levelsunderneath and extends downwardly an appropriate amount to meet the topof the armature. In FIG. 4, it can be seen that the lower edge of theabutment 14 is very slightly curved downwardly (see thick line) in thecenter just a sufiicient amount to just barely clear the armature. Thisallows the armature to ride flat on its knife edge bearing 31 withoutbinding as seen in FIG. 1, and yet be properly held in position.

At the front of the housing is an arched cross-bridge 18 which extendsfrom side to side. Running along each side of the housing 10 on theinside are ribs 19. Each of these ribs 19 connects the archedcross-bridge 18 with the corresponding vertical boss on its side of thehousing. To give added strength, the ribs 19 have raised edges near thefront and leading into the sides of the upper floor of the arched crossbridge 18 as best seen in FIG. 5.

Another flat cross-bridge 20 connects the sides of the housing 10 at thefront thereof, and this cross-bridge 20 also has ribs 21 extendingbackwardly along the sides to the corresponding vertical bosses 15.

At the bottom of the housing 10 is a compartment for receiving the testfingers 64 which compartment is provided with the enclosing flat bridge22 located at the bottom of the vertical boss 15. A vertical rib 23 nearthe center of the compartment runs the length of it to give stability.Similar ribs 29 are located at each side of the compartment for the samereason. Within the two smaller compartments are pairs of grooved ribs24, 25 and 26. At the back of this lower compartment, located a shortdistance inwardly is a horizontal enclosing rib 27 having these verticalslots seen in FIG. 4.

The upper portion of the housing structure 10 is a honeycomb or latticestructure which forms the back stops 70 for the fixed contacts and alsothe seats 71 for the coil springs biasing such contacts. Spaces 72 arealso provided for the movement of the movable contacts. At the bottom ofthis honeycomb there are two grooved spaces 73 for receiving pairs ofcoil connector fingers. A seat 75 is also provided for the armaturebiasing coil spring 48. In the four corners of the housing 10 are bossesfor receiving self-tapping screws adapted to secure the cover 11 inplace.

The inside of the honeycomb or lattice structure has two furtherinwardly projecting ribs 76'for giving added strength to the latticestructure and also for limiting the inward position of the contact guideblock 40. These two ribs 76 extend downwardly from the top of thehousing 10 to the slot 77. An intermediate slot 78 'also connects thetwo vertical ribs 76 which are in line from the front of the latticestructure to the near mid portion of the contact compartment.

With the above general understanding of the housing structure, it can bereadily seen that the cores 30 can have their pole pieces 33 and 34fitted into recesses in the vertical bosses 15. Also, a knife edgebearing plate 31 can be placed in the recess between thecross-bridge 16and the ribs 19, so as to receive the armature 35. The coded back plate36 is placed over the compartment and rivets 37 are slipped through thepole pieces 33 and 34, the bosses 15 and the coding plate 36. Theflattening of the heads of these rivets 37 thus secure the core pieces30, the armature and its bearing 31, the coded back plate 36 inposition. The core pieces 30 thus extend outwardly toward the front ofthe housing 10. The armature 35 has two vertical slots, one on eachside, which are slightly wider than the bearing strip 31 (see FIG. 6).The position shown in FIG. 6 is with the armature in its attractedposition at which time the armature lays flat against the flat plasticresidual strips on the pole faces. Such strips are placed on the polefaces just before they are fitted into the vertical bosses 15. With thearmature in this position, the entire slot of the armature is requiredfor the sides of the bearing which merely enter the slots which is bestseen in FIG. 7. The right-hand side of the bearing plate is in exactalignment with the left side of the armature. The coil button 46 is alsoslipped into its receiving hole in the armature 35A.

The contact guide block 40 is slipped into the upper portion of thehousing structure 10 and is held in position against the back of thelattice structure by placing the contact mounting block 42 in positionwhere it is held by inserting three self-tapping screws 43.

The fixed contact fingers 39 are slid into appropriate spaces in thelattice structure and enter the contact guide chute 44 in the contactguide block 40. Upon the further insertion of the contact, it is guidedto enter its slot in the mounting block 42. When a sufiicient portion ofthe finger exits through the slot in the block 42, a tool is insertedinto the recess at the rear of block 42 adjacent the slot and is used topull it through until the lock finger 45 springs downwardly and holdsthe contact in place. This fit of the contact 39 in the block 42 is snugand tight on both the upper and lower surfaces of the contact andparticularly so with regard to the side edges. It is the snug slot inthis block plus the continuing longitudinal sliding portions into theblock which determine the relatively exact perpendicular projection ofthe forward end of the contact finger 39. When the fixed contacts arepositioned, then the movable contacts 59 are similarly slid into theirpositions where they lock in place. When all of these contacts are inposition, suitable coil springs 41 are placed on their seats in thelattice structure for biasing the fixed contacts to their appropriatenormal positions. In addition, insulated seat 46 is inserted into a hole47 in the armature and a biasing spring 48 slipped into position ontothe two opposing seats 46 and 75.

The winding connector fingers 49 are slipped into position the same asthe other contact fingers, but these contact fingers merely extendforwardly for receiving quick detachable connectors 50.

When all of the fingers have been placed in position, the contact pushermember 51 shown in front view of FIG. 8 is positioned over the armaturearm 35A and gently laid against the movable contacts which may needslight adjustment in order to enter the slots in the extending fingers91 and 92 of the contact pusher member. These fingers 91 and 92 graspeach of the movable contacts exactly opposite their contact makingpoints so that such contacts are forceably moved by operation of thearmature removing any tendency of the contacts to burn closed as thepusher member 51 is moved by the armature.

When the pusher member 51 is moved inwardly so that it abuts against thecontact side extensions, then a lock finger 53 is inserted which hasprojections at its outer end for holding the pusher member 51 inposition. This lock finger 53 has the same kind of locking fingers 45for the contact block 42 as previously described.

The coils are wound on plastic spools 38 which readily slide over thecore members 30 with the coil ends suitably positioned and having thequick detachable contact members 50 attached at their ends. Thus, thetwo coils can be slipped over their respective cores 30 and their fourterminals suitably connected to their respective fingers 49 ratherquickly through appropriate spaces left in the contact pusher member 51.The outer ends of the spools 38 have a raised portion at one side. Theseraised portions are placed at the top and the bottom of their respectivespools so that a back yoke 62 can he slipped over the ends of the cores.This fit of the back yoke 62 is snug so as to make ready magneticcontact with the cores 30. This back yoke 62 is molded from powderedmagnetic material which is amalgamated into a unitary structure whichhas high magnetic permeability.

A spring 63 is located in a suitable space on the cover for contactingthe back yoke 62 and holds it firmly in position, when the cover isplaced in position. The test fingers 64 may have to be slightly adjustedto enter their respective slots in the cover.

When the cover is in position, the screws 65 are inserted to hold thecover 11 onto the housing 10. When the relay is thus constructed, it iscomplete and ready for operation.

To place it in operation, it is merely mounted on a plug board adaptedto receive its projecting contact fingers and having coded projectionsto enter the coded holes in the coded back cover 36. A wire bail 60 isconnected in the slot on the terminal board and is sprung over the outerhandles'81 of the relay as shown in FIG. 9. In this way the relay isheld on the terminal board and is removable when desired.

It is noted that FIG. 8 shows an enlarged front view of pusher member 51which can also be found in FIGS. 1 and 2. This front view shows theextending lips 91 and 92 which take hold of the contact fingers directlyadjacent the contact points as can also be seen in FIGS. 1 and 2. Also,mild shading is shown in areas of FIG. 8 to illustrate the thin webs 93of molded material between major portions or bars of the material. Thesethin web portions 93 act to give strength and stability to the pushermember 51. The larger fingers 94 act to grasp the armature arm 35A ascan be seen in FIG. 2. (It is noted that one of these fingers 94 isomitted from FIG. 2.)

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein, without departing from the invention; and, it is, therefore,intended that the appended claims shall cover all such changes andmodifications as fall within the true spread and scope of the invention.

What we claim is:

'1. An electromagnetic relay having a plurality of contacts wherein theimprovement comprises a rectangular box shaped housing substantiallyopen on the inside thereof with openings at the front and back and withthe other sides completely enclosed, an electromagnetic structurelocated in the lower portion of said housing and having an L-shapedarmature cooperating therewith, one arm of said armature cooperatingwith said electromagnet at the rear of the relay to form a workingairgap, and the other arm of said armature extending forwardly throughthe mid portion of said housing, whereby said armature is gravity biasedto normally open said working airgap, electrical contacts mounted in theupper portion of said housing, and a pusher member operated by saidother arm of said armature for operating said contacts, the housinghaving formed integral therewith at the front of the relay a latticestructure for supporting one end of the contacts that are fixed in thatthey are not subject to actuation by the armature.

2. A relay according to claim 1 in which a lattice structure is locatedin the upper portion of said housing with said electrical contactsmounted therein, and a coil spring mounted between said latticestructure and said armature for additionally biasing said armature.

3. A relay according to claim 1 in which said armature is mounted on aknife-edge bearing near its center, which is secured to the housing andin which the housing has a cross-bridge with an underhanging abutmentdirectly over said armature above said knife-edge bearing.

4. A relay according to claim 1 in which said armature is mounted on aknife-edge bearing near its center, which is secured to the housing andin which the housing has a cross-bridge between the sides of saidhousing above said bearing and having an underhanging abutment, saidabutment having a very slight arcuate portion across said armature andbarely failing to touch said armature at its center.

5. A relay according to claim 1 in which said forward end of saidarmature is supported by an arched bridge portion of the housingconnecting the two sides of said housing.

6. A relay according to claim 1 in which said forward end of saidarmature in its released position is supported by an arched cross-bridgemember connected between the sides of said housing, and a coil springbetween said armature and another cross-bridge member for biasing saidarmature toward said arched crossbridge.

7. In a relay, a housing structure of rectangular box shape andgenerally open on the inside thereof, the front and back portions ofsaid structure being substantially open and the other sides thereofbeing completely enclosed, electrical contacts mounted in the upperportion of said structure and an electromagnet in the lower portion ofsaid structure and having two cores with parallel pole faces at the backthereof, an L-shaped armature mounted on a knife-edge bearing inalignment with said pole faces so as to have one arm of said armature ina working airgap with said pole faces and the other arm extendingthrough the central portion of said structure and operatively connectedto said contacts, windings on said two cores, and a slip-on type backyoke having holes for snugly receiving said two cores, and a cover forenclosing the front side of said relay with a spring means mountedthereon for holding said back yoke in position.

8. In a relay as specified in the claim 7 wherein said windings haveextending coil connections with quick detachable connectors mountedthereon, said quick detachable connectors being connected to coilconnector fingers running fromfront to the back of said relay.

9. In a relay: structure as specified in claim 7 wherein there arebosses running vertically along the back edge of the lower portion ofsaid housing structure, and wherein said core members are mounted on thefront of said bosses and a coded back plate is mounted at the rear ofsaid relay on said bosses and said core and 'back plate being riveted tosaid bosses by the same rivets, said coded back plate having holesarranged in a coded configuration.

10. In a relay structure as specified in claim 7 wherein a spacedcompartment is located at the bottom of the relay having grooved ridgesrunning through an enclosed space for receiving test fingers each havingconstricted projections at each end, the projections at one end forpassing through slots at the rear end of said compartment and theprojections at the other end for passing through slots in said cover.

11. In a relay, a rectangular box shaped housing substantially open onthe inside thereof with openings at the front and back and with theother sides completely enclosed, said housing being molded of a fireresistant plastic resin, and having a lattice framework in the upperfront of the structure with cross members and with spaces, a slottedcontact mounting block located within said housing at the rear thereof,said slots being located to match the spaces in said lattice framework,fixed and movable contact fingers mounted in said slots of said contactmounting block and extending through said lattice framework, anelectromagnetic structure located in the lower portion of said housingand having an L-shaped armature cooperating therewith, said armaturehaving one arm cooperating with said electromagnet at the rear of therelay to form a working airgap, and the other arm of said armatureextending forwardly through the mid portion of said housing, a pushermember operated by said other arm of said armature and connected to saidmovable contacts, coil springs mounted in said lattice work for holdingsaid fixed contacts against their respective cross members, and a coilspring between said lattice work and said armature for biasing saidarmature to open said working airgap, said core structure extendingforward in the relay and having mounted thereon energizable coils, asintered back yoke snugly fitted over said core members but removabletherefrom, and a cover for enclosing the front 9 10 side of said relaywith a spring means mounted thereon 3,076,880 2/1963 Ehrismann 335128for holding said back yo ke in position. 3,270,301 8/1966 Bengtsson335-129 References Cited BERNARD A. GILHEANY, Primary Examiner UNITEDSTATE P TEN 5 H. BROOME, Assistant Examiner 990,032 4/1911 Clement335128 2,134,448 10/1938 Knos 335-129 5 2 2 2,556,716 6/1951 Viol335-129 33 0 3,001,049 9/1961 Didier 335-136

